1. Field of the Invention
The present invention relates to a method for continuously cutting off successive pieces or sections from a continuously moving endless material by flying cutting by means of a cutting apparatus or device accelerated to the speed of the endless material, which is synchronized for each piece or section. It also relates to a cutting apparatus for performing the method.
2. Prior Art
Products in various industrial fields are often available initially in the form of continuously moving endless material, typically as a band or strip. These fields include e.g. flat glass manufacture, steel, aluminum or other metal production or processing fields, certain parts of the plastic industry (for example foil manufacture) and areas of the food industry. In each application the continuously moving band or strip must be cut into predetermined lengths, pieces or sections. The line of the cutting is generally perpendicular to the motion direction of the endless material, i.e. the belt or strip edge.
In order to avoid interruption of the continuous motion of the endless material and so that processing time is not increased, the cutting away of the pieces or sections is performed in a known manner according to the principle of xe2x80x9cflying sawingxe2x80x9d. According to the principle of xe2x80x9cflying sawingxe2x80x9d a portal or frame, in which a cross-cut slot is provided with a cutting tool, the so-called cutting bridge, is accelerated to the speed of the endless material. As soon as the speed of the endless material is reached, cross-cutting is initiated. Thus the endless material is cut so as to form a rectangular piece or section of the endless material. Subsequently the bridge is moved back into its initial position.
The adjustment of the speed of the cutting bridge to the speed of the endless material occurs typically by means of a controller. The controller establishes a certain predetermined set speed (V-set) for the drive system of the cutting bridge. The controller must also set the exact time point at which the synchronous motion is started. A difference between the actual speed (V-act) and the set speed (V-set) of the cutting bridge or an inexact starting time for the cutting causes inaccurate cutting. The cutting speed of the cutting bridge is the greatest source of factors interfering with the accurate cutting away of the pieces or sections from the endless material.
It is an object of the present invention to provide an improved method for cutting away successive pieces or sections from a continuously moving endless material of the above-described type, which cuts the pieces or sections with an accuracy in the {fraction (1/100)} mm range.
It is also an object of the present invention to provide an improved cutting apparatus for performing the improved method according to the invention.
The method according to the invention for continuously cutting away successive pieces or sections from a continuously moving endless material by flying cutting by means of a traveling cutting device accelerated to the speed of the endless material, which is synchronized for each piece or section, comprises the steps of:
a) producing a pre-control speed value for pre-controlling a cutting device travel speed to bring it within a synchronization range of a feed speed of the continuously moving endless material;
b) pre-controlling the cutting device travel speed according to the pre-control speed value until it is within the synchronization range; and
c) then generating a control signal for fine regulation of the cutting device travel speed; and
d) controlling the cutting device travel speed by means of a cutting device travel speed controller according to the control signal for fine regulation so that each piece or section is cut to a predetermined piece or section length;
wherein the actual value of a distance of the front cut edge of the endless material from which a previous piece or section was cut to the cutting device is measured, a set value of the distance corresponding to the predetermined length of the next piece or section to be cutaway is compared with this actual value and the difference between the set value and the actual value is calculated, the speed of the traveling cutting device within the synchronization range is then fine-tuned or controlled by increasing it or decreasing it by means of the speed controller according to the comparing when there is a difference and the next piece or section is cut away when the set value agrees with the actual value.
The above-described objects of the invention are also attained in an apparatus according to the invention that includes a conventional traveling cutting bridge, which has an elongated carriage that travels in the motion direction of the endless material and a transversely traveling carriage with a cutting tool that is mounted on the elongated carriage, which are accelerated for flying cutting by drive means and are synchronized to the feed speed of the continuously moving endless material.
According to the invention the apparatus has a camera device mounted on the cutting bridge at a predetermined distance from the cutting tool, which corresponds to a length of the next piece or section to be cut away, and control means for the drive means are provided. The control means comprises means for analyzing image signal produced by the camera device and for producing control signals for the drive means for controlling the acceleration of the cutting bridge according to the analysis of the image signals.
The principal features of the invention are that the speed of the cutting device is brought within a synchronization range of the speed of the endless material and after that the speed of the cutting device is fine-tuned or adjusted according to the length of the given piece or section. Because of these features the accuracy of the cut piece or section is within {fraction (1/100)} mm.
According to a preferred embodiment of the inventive method both the distance of the front cut edge from the cutting tool is measured and the subsequent fine control of the speed synchronization are also performed during the cutting of the endless material. After the cutting is complete they are interrupted or halted until activation or initiation of a following cutting process. Because of this feature a high precision of the cutting process is also maintained during the cutting of the endless material.
The control expense and effort can be limited according to a preferred embodiment of the method according to the invention when the distance of the front cut edge from the cutting tool is measured and the subsequent fine control of the speed synchronization are started as soon as the cutting device is within the tolerance range for the cutting to be performed.
An especially simple control of the cutting away process can be obtained according to a preferred embodiment of the invention by a position control, in which the front cut edge of the endless material is imaged on a camera device moving with the cutting device, the measured position of the image of the cut edge is compared with a position set value and the speed of the cutting device to be synchronized is subsequently controlled according to a deviation of the measured position from the position set value and the cutting away is initiated or started when the measured position agrees with or corresponds to the position set value.
In order to provide a rapid fine control, it is performed digitally and iteratively in successive steps according to a preferred embodiment of the invention. Also an analog control is conceivable.
According to another embodiment the apparatus according to the invention is formed so that the camera device is a high-speed-partial-scan camera and the controller is a digital controller, in which associated image analysis software is provided. This sort of arrangement guarantees the necessary rapid detection of the front edge of the continuously moving endless material and the rapid fine control.
An analog controller can also be employed.
According to another embodiment of the apparatus a camera device comprising a camera with integrated processor is provided. In this case the external image processing software and associated processor can be dispensed with.
An especially fine control is possible when the camera device is a streaking camera with connected comparing device in an alternative embodiment of the apparatus according to the invention.
In a further embodiment of the apparatus according to the invention an illuminating device is arranged on the cutting bridge to provide better optical detection of the front cut edge of the endless material. The illuminating device illuminates the view field of the camera device.